Devices of the type mentioned above already exist.
Note that generally speaking, breathing assistance devices are designed to provide a patient with respiratory assistance, using a source of gas (oxygenated mixture) which can be connected to a turbine.
These devices can be sorted into two main categories:
(a) Ventilators. These devices are of the barometric type and realize ventilation through leakage (via vents on the mask located on the patient side),
(b) Respirators. These devices include an expiratory valve to realize ventilation without leakage. They include a “simple” circuit (a single duct between the patient and the device), or double.
Ventilators operate with a single duct between the device and the patient. This single duct finishes on the patient side with a vented mask, allowing leakage.
Ventilators generally operate in a mode of the “barometric” type according to which the inspiratory and expiratory phases are mainly triggered by pressure measurements.
Note that in general, certain breathing assistance devices can operate in a mode of the volumetric type (in which the devices forces a given quantity of air into the duct).
The operating modes will be discussed further in this text.
Ventilators are of the CPAP type or of the BPAP type.
The CPAP type (acronym for the Anglo-Saxon denomination Continuous Positive Airway Pressure—this type can also be designated by the acronym PPC, for Pression Positive Continue) designates ventilators with a single pressure level.
In these ventilators, turbine speed is regulated by a pressure measurement in the single duct.
The single pressure setting is generally set to a value less than 20 mbars (this value is expressed as excess pressure in relation to atmospheric pressure), which limits the use of such ventilators to treating superficial pathologies.
Ventilators of the BPAP type (acronym for the Anglo-Saxon denomination Bilevel Positive Airway Pressure, this acronym is a registered trademark—and this type can also be designated by the acronym VNDP for Ventilation Nasale a Deux niveaux de Pression) using the same general architecture, but operating with two pressure settings (a value for inspiration pressure and a value for expiration pressure).
Regulation of the device is in this case generally controlled by:
Pressure measurement in the duct, or
Flow measurement in the duct.
This regulation can be applied to:
Turbine rotation speed (as in the case with CPAP ventilators), or
The opening of an optional rate valve which is located on the duct.
The pressure setting is generally set to a value less than 30 mbars, which allows treating pathologies that are a bit more extensive than the CPAP.
The second category is that of expiratory valve respirators.
These devices operate with, on the patient side, a mask without vents and an expiratory valve allowing the gas expired by the patient to be directed out of the device (for example into the surrounding atmosphere), in order to avoid reflux of the gas expired into the duct carrying the gas to the patient.
These respirators are of the barometric or volumetric type.
Barometric respirators are regulated by a pressure setting, the setting can have two different values.
These devices operate therefore according to the repetition of two phases: an inspiratory phase and an expiratory phase. A different value for the pressure setting is assigned to each phase.
These phases are initiated according to pressure or flow measurements.
A flow sensor is integrated into the respirator, in order to follow the volume of gas inhaled by the patient.
The values for pressure settings can be higher than in the case of ventilators for ventilation via leakage: these values can reach about 120 mbar.
Volumetric respirators also operate according to a succession of inspiratory and expiratory phases.
But in this case, a volume of gas defined beforehand must be delivered to the patient by the deliverance of a corresponding flow—the phases are therefore initiated according to the measure of the flow inhaled by the patient, with pressure being a resulting variable and not a controlling variable.
The source of gas is frequently with this type of respirator a bellows or piston apparatus.
It is however also possible for the source of gas to be a turbine. In this case, it is necessary to have fine control of turbine operation.
We have seen above that breathing assistance devices fall into different categories, and that different operating modes are associated with them.
We shall call these different operating modes “respirator modes”.
A respirator mode is thus defined by the control variables, controlled variables, but also by the material means implemented (type of duct between the device and the patient, presence or not of an expiratory valve, of pressure sensors in different locations of the device, etc.).
Furthermore, note that there are hybrid devices, providing different operating modes with the same device.
WO 96/11717 demonstrates for example a device in which it is possible to select different respirator modes, using a control panel 320.
The possibility to access different respirator modes with a single device is certainly interesting.
But the device can become complex to handle, because of the different modes that are possible.
In fact, for each respirator mode it can be necessary to adapt the device, by connecting/disconnecting certain parts (such as mentioned above: type of duct, valves, sensors, etc.).
And the known hybrid devices expose patients to incoherencies between a chosen mode and the configuration of the device (in particular concerning parts that are connected to the device).
In fact, the multiplication of respirator modes on the same device also multiplies the risk of manipulation error, since the device can be programmed for a given respirator mode although the correct connections for this mode are not realized.
These incoherencies at best lead to complex implementation (obligation to reconfigure the device), and at worst a danger for the safety of the patient.